It is well known in the art of fuel supply to internal combustion engines that finer atomization and more even fuel distribution into the intake air result in lower specific fuel consumption, especially in multi-cylinder engines. With conventional carburetors, fuel atomization and distribution at larger engine loads is often much less than optimal. The typical carburetor employs a butterfly-type throttle valve for flow modulation, and has a large load fuel to air admixture nozzle that consists of a fuel outlet located in the inlet airstream centrally in a venturi constriction portion of the inlet.
For large load but less than full load engine operating conditions, the throttle valve is at a steep angle in the air inlet. Air flowing through the inlet upstream from the throttle must divide to flow past the partially open throttle. The lateral air movement in the air inlet to achieve this division occurs more upstream in the inlet the closer the air is to the inlet periphery. Air flowing in the center of the inlet airstream does not undergo lateral movement until just immediately above the throttle plate.
Centrally located large load fuel outlets are typically constrained by physical size to be as compact as possible. Thus, they are often at a disadvantage in their ability to involve a large mass of air at the contact point of fuel to air admixture. The resulting poor atomization means that there are large fuel droplets that are entrained in the center part of the inlet flow. As previously mentioned, the flow in the center part of the inlet does not divide for partial throttle operation until immediately above the angled throttle plate. The result of this is that majority of the entrained fuel escapes symmetrical lateral flow action, but is instead influenced by the slant of the partially open throttle plate. As a consequence, the majority of the entrained fuel is directed towards the downstream angled part of the throttle plate Thus, the fuel distribution downstream from the throttle plate is less than optimal, there being a strong biasing of the fuel towards one side of the air inlet.
A few previous attempts to overcome some of these problems had a main fuel nozzle which introduced the large load fuel into the air inlet through a series of outlet holes or ports equally spaced about the periphery of the air inlet, at or just below the venturi constriction. This theoretically can entrain the fuel in the peripheral airflow in the inlet, where there is the soonest and greatest lateral flow near the partially open throttle, hence the least biasing effect due to the throttle plate angle.
These previous attempts did not meet with much success, however, for several reasons. One is that fuel atomization was not very good, due partially to the stagnant layer of air near the intake walls. Although admixture mass was large, air speed was low. Also, fuel flow out of the outlet ports nearest the supply duct tended to be much greater than fuel flow from the outlet ports most remote from the supply. This resulted in a very unfavorable bias at or near wide open throttle. Also, locating the peripheral ports around the most narrow part of the conventional venturi constriction did not ensure that the ports would all open into the minimum pressure area, or that the pressure reduction at all of the port openings would be the same. These inconsistencies exerted an adverse effect on fuel metering and distribution.
In comparison with previous peripheral constructions, a conventional centrally located compound venturi booster nozzle, with its very high air speed, gave better overall results.
Additionally, the present invention provides a fuel to air admixture construction which acts to minimize or prevent altogether the tendency for fuel to leave the fuel/air mixture and be deposited onto the air inlet walls. The divergent configuration of the walls of the air inlet causes the fuel to move relatively away from the inlet walls while flowing through the air inlet.
The present invention provides a peripheral main fuel nozzle which overcomes the problems of previous designs, thereby affording the advantages of large air mass at the point of admixture, fuel entrainment in the peripheral airflow, and the additional advantage of very high air speed at the point of admixture. Furthermore, the smaller dimensions of the peripheral venturi provide more consistent and reliable pressure reduction signal for the main fuel metering means.
The carburetor of the present invention is simple and easy to construct, employing to advantage the manufacturing techniques and tooling currently used to manufacture carburetors. The design even lends itself well to retrofitting carburetors already manufactured or in service.